Environmental tobacco smoke, cardiovascular disease, and the nonlinear dose-response hypothesis.
(17/1807)
Two recent government reports have focused attention on the hypothesis that environmental tobacco smoke (ETS) exposure increases the risk of cardiovascular disease (CVD) in nonsmokers. The first report was published by the California Environmental Protection Agency (CAEPA) in 1997. The second report was issued in 1998 by the Scientific Committee on Tobacco and Health (SCOTH) in the United Kingdom. A meta-analysis of five large prospective epidemiology studies reports that the relative risk for actively smoking 20 cigarettes per day is 1.78. Active smoking exposes the smoker to approximately 16 times the ETS concentration, and 100- to 300-fold the total smoke dose experienced by a nonsmoker (Smith and Ogden, 1998, JAMA 280, 32-33.). Despite the much lower smoke exposure, these government reports estimate the relative risk for ischemic heart disease in ETS-exposed nonsmokers at 1.30 (CAEPA) and 1.23 (SCOTH). As an explanation for this nonlinear dose-response anomaly, platelet aggregation is proposed to be a plausible and quantitatively consistent mechanism. Herein, evidence is presented suggesting that this low-dose hypothesis is inconsistent with the biochemistry and physiology of platelets and with the literature on the cardiovascular pathology of active smoking. In addition, several important biases and confounders are ignored. These epidemiologic biases and confounders include the following: misclassification of smokers as nonsmokers; improper use of death certificates as surrogates for mortality statistics; underreporting of diabetes and hypertension in the relatives of smokers; and additional atherogenic risk factors in smoking households. Future field studies on ETS and CVD should emphasize proximal markers of risk for thrombosis in exposed nonsmokers. Proximal thrombogenic risk markers identified in field studies should be mechanistically examined under controlled exposure conditions. (+info)
The effect of home visiting programmes on uptake of childhood immunization: a systematic review and meta-analysis.
(18/1807)
BACKGROUND: The aim of the study was to evaluate the effectiveness of home visiting programmes on the uptake of childhood immunization. METHODS: A systematic review was carried out of the literature of controlled studies evaluating home visiting programmes involving at least one post-natal visit, which included tasks within the remit of British health visiting and reporting outcomes relevant to British health visiting. Eleven studies were considered, nine of which used socio-economically disadvantaged families. The outcome measure was uptake of a range of childhood immunizations. RESULTS: Eleven studies reported uptake of immunization. Effect sizes from nine studies were included in the meta-analysis. Fixed effects models demonstrated a significant effect of home visiting for all studies and also for several subgroups of studies, but with significant heterogeneity of effect sizes. A random effects model failed to demonstrate an effect of home visiting. CONCLUSIONS: Home visiting programmes have not been shown to be effective in increasing the uptake of immunization. Other methods of increasing uptake and reducing inequalities in uptake will need to be explored. (+info)
Quantitative trait loci: a meta-analysis.
(19/1807)
This article presents a method to combine QTL results from different independent analyses. This method provides a modified Akaike criterion that can be used to decide how many QTL are actually represented by the QTL detected in different experiments. This criterion is computed to choose between models with one, two, three, etc., QTL. Simulations are carried out to investigate the quality of the model obtained with this method in various situations. It appears that the method allows the length of the confidence interval of QTL location to be consistently reduced when there are only very few "actual" QTL locations. An application of the method is given using data from the maize database available online at http://www. agron.missouri.edu/. (+info)
Caffeine during pregnancy? In moderation.
(20/1807)
QUESTION: Many of my female patients, those who plan pregnancy or have conceived, are afraid of any intake of caffeine. This often makes their lives miserable during pregnancy. Is this justified scientifically? ANSWER: Motherisk's recent meta-analysis suggests that the risks for miscarriage and fetal growth retardation increase only with daily doses of caffeine above 150 mg/d, equivalent to six typical cups of coffee a day. It is possible that some of this presumed risk is due to confounders, such as cigarette smoking. (+info)
Graft material and results of platelet inhibitor trials in peripheral arterial reconstructions: reappraisal of results from a meta-analysis.
(21/1807)
AIMS: To investigate the characteristics of published trials in order to establish the origin of the differing results obtained in trials of platelet inhibitors after peripheral bypass procedures. METHODS: Analysis of the information from 11 randomised, controlled trials of platelet inhibitors after peripheral bypass procedures published up until 1999 and involving 2302 patients undergoing peripheral bypass operations, 1250 of whom were treated with platelet inhibitors. RESULTS: There is a significant treatment benefit of platelet inhibitors on meta-analysis of the trials, but a significant heterogeneity amongst the individual trial results. The proportion of patients in a trial with prosthetic grafts was a significant factor in explaining the heterogeneity. Proportion of prosthetic grafts was associated with sample size and with the proportion of grafts above the knee, but these were not found to make an independent contribution to the heterogeneity observed. The platelet inhibitor regimen used, the severity of ischaemic symptoms and the proportion of smokers included were also not found to be important. CONCLUSIONS: The improvement of graft patency by aspirin and related platelet inhibitors in clinical trials in peripheral bypass procedures can be attributed to an effect on patients with prosthetic grafts. There is little evidence that these agents prevent occlusion of vein grafts. The conclusion of an earlier meta-analysis that antiplatelet agents should be used for all bypasses is not supported. (+info)
Prospective cohort study to determine if trial efficacy of anticoagulation for stroke prevention in atrial fibrillation translates into clinical effectiveness.
(22/1807)
OBJECTIVE: To determine whether trial efficacy of prophylaxis with warfarin for patients with atrial fibrillation at high risk of stroke translates into effectiveness in clinical practice. DESIGN: Two year prospective cohort study. SETTING: District general hospital. PARTICIPANTS: 167 patients with atrial fibrillation and at high stroke risk who were eligible for anticoagulation. INTERVENTIONS: Long term anticoagulation with warfarin at adjusted doses to maintain an international normalised ratio of 2.0-3.0. MAIN OUTCOME MEASURES: Comparison of patient characteristics, comorbidity, anticoagulation control, stroke rate, and haemorrhagic complications with pooled data from five randomised controlled trials. RESULTS: Patients in the study group were seven years older (95% confidence interval 4 to 10) and comprised 33% more women than patients in the pooled trials. The international normalised ratio was in the target range for 61% of the time (range 37%-85%), below for 26% of the time (range 8%-32%), and above for 13% of the time (range 6%-26%). The time that patients in the study group spent in the target range was significantly less than in the pooled analysis. The incidence of stroke in the study group (2.0% per year, 0.7% to 4. 4%) was comparable to that of patients receiving warfarin in pooled studies (1.4%, 0.8% to 2.3%). Per year the incidence of major (1.7% v 1.6%) and minor (5.4% v 9.2%) bleeding complications was also similar. CONCLUSION: Rates of stroke and major haemorrhage after anticoagulation in clinical practice were comparable to those obtained from pooled data from randomised controlled studies for patients with atrial fibrillation at high risk of stroke. (+info)
Manipulation of host behaviour by parasites: a weakening paradigm?
(23/1807)
New scientific paradigms often generate an early wave of enthusiasm among researchers and a barrage of studies seeking to validate or refute the newly proposed idea. All else being equal, the strength and direction of the empirical evidence being published should not change over time, allowing one to assess the generality of the paradigm based on the gradual accumulation of evidence. Here, I examine the relationship between the magnitude of published quantitative estimates of parasite-induced changes in host behaviour and year of publication from the time the adaptive host manipulation hypothesis was first proposed. Two independent data sets were used, both originally gathered for other purposes. First, across 137 comparisons between the behaviour of infected and uninfected hosts, the estimated relative influence of parasites correlated negatively with year of publication. This effect was contingent upon the transmission mode of the parasites studied. The negative relationship was very strong among studies of parasites which benefit from host manipulation (transmission to the next host occurs by predation on an infected intermediate host), i.e. among studies which were explicit tests of the adaptive manipulation hypothesis. There was no correlation with year of publication among studies on other types of parasites which do not seem to receive benefits from host manipulation. Second, among 14 estimates of the relative, parasite-mediated increase in transmission rate (i.e. increases in predation rates by definitive hosts on intermediate hosts), the estimated influence of parasites again correlated negatively with year of publication. These results have several possible explanations, but tend to suggest biases with regard to what results are published through time as accepted paradigms changed. (+info)
Does home visiting improve parenting and the quality of the home environment? A systematic review and meta analysis.
(24/1807)
AIMS: To evaluate the effectiveness of home visiting programmes on parenting and quality of the home environment. DESIGN: Systematic review of the literature of randomised controlled trials and quasi-experimental studies evaluating home visiting programmes involving at least one postnatal visit. SUBJECTS: Thirty four studies reported relevant outcomes; 26 used participants considered to be at risk of adverse maternal or child health outcomes; two used preterm or low birth weight infants; and two used infants with failure to thrive. Only eight used participants not considered to be at risk of adverse child health outcomes. RESULTS: Seventeen studies reported Home Observation for Measurement of the Environment (HOME) scores, 27 reported other measures of parenting, and 10 reported both types of outcome. Twelve studies were entered into the meta analysis. This showed a significant effect of home visiting on HOME score. Similar results were found after restricting the analyses to randomised controlled trials and to higher quality studies. Twenty one of the 27 studies reporting other measures of parenting found significant treatment effects favouring the home visited group on a range of measures. CONCLUSIONS: Home visiting programmes were associated with an improvement in the quality of the home environment. Few studies used UK health visitors, so caution must be exercised in extrapolating the results to current UK health visiting practice. Further work is needed to evaluate whether UK health visitors can achieve similar results. Comparisons with similar programmes delivered by paraprofessionals or community mothers are also needed. (+info)